Conventionally, a technology is disclosed in which a blade where a sharp-pointed protrusion whose upper end is smaller in width than the tip end surface of the blade and whose angle is acute is integrally formed and where a relief groove portion is formed at an intermediate place in the tip end surface on a front side of the blade in a rotation direction is provided and in which the sharp-pointed protrusion is melted to weld a front plate (shroud) to the blade (see Patent Document 1).
It is thought that in the technology of Patent Document 1, the relief groove portion is provided to prevent the production of flash caused by the welding, and the flash caused by the welding in the entire blade can be completely removed at the time of completion, with the result that it is possible to enhance productivity (manufacturing efficiency) and product quality.
A technology is also disclosed in which a shroud and a blade opposite the shroud are joined with a joint portion which is formed with a horizontal flat portion provided in the rear edge portion and the front edge portion of the blade or the center portion thereof and an inclined flat portion provided between the horizontal flat portions (see Patent Document 2).
It is thought that in the technology of Patent Document 2, the shroud and the blade are joined with the horizontal flat portion and the inclined flat portion, and when they make contact with each other, it is possible to accurately achieve close contact without any gap, with the result that this part is accurately welded by high-frequency waves to acquire sufficient welding strength.    Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2010-236495    Patent Document 2: Japanese Unexamined Patent Application, Publication No. 2009-257132